Recent development of communication technologies has resulted in mobile devices being used for different functions. Different user interfaces have been provided, wherein a most predominant user interface is based on touch-sensitive screens or touch screens. Many different technologies have been used to unlock a mobile device for usage; i.e., granting access to the mobile device's functions. Typically, mobile devices that are smart devices are put into a sleep mode if not used in order to prevent unintentional reception of signals from the touch screen if the device is, e.g., in a pocket of the user. In order to set the mobile device again into an active mode, often a PIN (personal identification number) has to be typed in if a slider is to be moved or activated.
However, in cases in which the mobile device (e.g., a smart phone with a (subscriber identification module) SIM card) may be used the first time, increased security standards have to be met. Hence, there is a need to increase the barrier for an unauthorized access to a mobile device or to other devices being equipped with a touch-sensitive screen.